Selection of riser size and location for large gray iron castings

The use of riser is one of the basic means to solve the shrinkage of casting. Although there are new views and new views on riser setting in recent years, the key role played by the team of zhycasting senior engineers has never been questioned.

In the actual production, the riser of large-scale iron castings can be divided into gas outlet riser, observation riser, slag discharge riser and skin shrinkage Riser Based on the purpose of use. Although the first three kinds of maoyue also have the function of shrinking prevention, their function plays a major role. According to different types of riser neck, the basic type of compression riser is divided into rectangular compression riser and top circular compression riser. In the actual operation, the compression riser is usually made by the riser bar, and the shape of the riser bar is shown in the figure. For the convenience of operation, other types of compression risers such as edge risers and waist risers are only variations of the two kinds of risers in a sense. Because the research object of this paper is mainly compression riser, so for the convenience of description, compression riser is called riser for short.

In recent years, with the development of riser research, special riser is used more and more widely. In traditional sense, the riser is made of the same material as the mold itself, because its thermal conductivity is the same as that of the mold, and the solidification time of molten iron in the riser is the same as that of the casting body, so its feeding efficiency is very low, generally between 6% and 10%. At the same time, in order to improve the feeding effect of the riser, it is often realized by increasing the riser diameter and height, so as to reduce the technological yield of the casting and increase the production cost. Therefore, how to reduce riser size and improve riser feeding efficiency under the condition of ensuring casting compactness is one of the main directions of riser research. At present, the solution of more research is to extend the solidification time of molten iron in the riser. Based on this principle, there have been insulation riser, heating riser and composite heating riser with the above two functions. It has been proved that the feeding efficiency of moisturizing riser is 20% – 25%, and that of compound heat preservation riser is 45%. However, the most widely used moisturizing riser in China is due to its cost.

The feeding principle of moisturizing mask is the same as that of common riser, but because the selected base material is relatively less than the heat conductivity of sand mold, it is equivalent to increasing the heat capacity of molten iron in the riser and reducing the heat dissipation area of the riser, thus ultimately extending the heat preservation time of molten iron. The author’s unit has also used heat preservation cap at the shrinkable position of some castings.

There is a large area of shrinkage porosity at the position of unused insulation riser, while the shrinkage porosity at the position of unused insulation riser is obviously improved, and there is no obvious porosity. From these two photos, it can be seen that the effect of insulation riser on the feeding of riser is obvious.

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